Boreskov

PROCARYOTIC ASSEMBLAGES OF EARLY PRECAMBRIAN (AR‐PR 1 )Astafieva M.M.Borissiak Paleontological Institute of Russian Academy of Sciences,Profsoyusnaya, 123, 117997 Moscow, Russia;Tel.: +7‐495‐339‐7911; FAX: +7‐495‐339‐1266; E‐mail: astafieva@paleo.ruOP‐25Recently our ideas about the most ancient stages (AR‐PR 1 ) of life evolution on Earthwere greatly expanded as a result of bacterial‐paleontological investigations. Widedistribution of fossil bacterial remains in ancient sedimentary and volcanogenic sequencestestifies that their assemblages were the most important factor of biosphere evolution andsedimentogenesis on the Earth surface beginning with Archaean.Almost all sedimentary rocks, except for rudaceous rocks, are deposited andtransformed during diagenesis with some participation of bacterial (microbial) constituent orother. At present it is known, that biogenic factor plays significant role in formation of suchmineral groups as native minerals, diverse sulphuric compounds, oxides, silicates,carbonates, phosphates, sulfates, tungstates and organic acids salts. Fossil microorganisms,biofilms and microbial mats are similar in morphology with modern bacteria, biofilms andmats.As exemplified by process of genesis of phosphorites and the ancient weathering crustsformation it is possible to infer that mechanism of rock and mineral formation remainedpractically unchanged through the whole Earth history from Archaean to Holocene.It is important to emphasize that almost all known mineral compounds of phosphorus inthe Earth crust are the salts of orthophosphoric acid H 3 PO 4 and that atmospheric oxygen isnecessary to form of this acid. Thus phosphorites, including Early Proterozoic ones, wereformed under conditions of rather warm shallow‐water basin with oxygenated waters.The most ancient (AR‐PR 1 ) microbial assemblages were confined to volcanogenicsediments of the past and to hydrothermal systems. As well as nowadays ancient bacteriallife thrived just after an eruption as the surface, covered with lava, became colder. Bacteria,including cyanobacteria, developed on the “lava – water” interface. Cyanobacterialassemblages formed and even some unicellular eucaryots probably existed. Moreoverquality and quantity of microbial assemblages of volcanogenic areas differed according toancient conditions.71